1. Field of the Invention
The present invention relates to a light quantity adjusting apparatus, a color-registration-deviation amount detecting apparatus, a light quantity adjusting method, and a color-registration-deviation amount detecting method that can make adjustment by simple procedures.
2. Description of the Related Art
In color image forming apparatuses, color registration deviation must be eliminated in output images of respective colors of magenta, cyan, yellow, and black so as to improve image quality. In quadruple tandem color image forming apparatuses that include a pair of a write optical system and an image carrier per color, images of the respective colors are formed by different pairs of optical systems and image carriers. Therefore, color registration deviation is particularly apt to occur. For correcting the color registration deviation, there is generally known a technique of writing a position deviation detection pattern on a transfer belt or the like, reading the pattern by a sensor to detect a deviation amount, and correcting the deviation amount by adjusting the write timing or with an optical system correcting unit.
For example, Japanese Patent Application Laid-Open No. 2001-318501 discloses a technique that is intended to detect a difference in reflectance between a color registration deviation pattern of each color transferred onto a carrier with a very small light quantity and the carrier itself and to correct a color registration deviation without being affected by a surface state and a transfer surface color of the carrier. A reference voltage for reading a plurality of color registration deviation detection pattern images through a regular reflection optical system based on a base reflecting state of a transfer belt detected by an optical sensor, which serves as the regular reflection optical system, is variably set. The reference voltage is compared with a signal output from the optical sensor, so that a controlling unit generates a pulse signal. The color registration deviation amount among the images of the respective colors is calculated based on the generated pulse signal, and image positions are controlled to be corrected by image forming stations for the colors other than the reference color based on the calculated color registration deviation amount.
Japanese Patent Application Laid Open Nos. 2003-228216, 2003-098795, and 2003-280317 also disclose known and related techniques.
However, according to the invention disclosed in Japanese Patent Application Laid Open No. 2001-318501, since it is necessary for a light quantity detector to read the output of each color registration deviation detection pattern without fail, a quantity of emitted light for irradiating the pattern must be adjusted to a desired level before the color registration deviation detection.
That is, according to the conventional technique, to adjust the light quantity, a processing of changing a set value of the light quantity and reading the output of each pattern is repeated a plurality of times before calculating the set value of the light quantity, at which the desired target output can be obtained. Therefore, adjustment of the light quantity takes a long time.